Traditionally field workers such as fire fighters and plant workers communicate using two way radios such as radios supplied by Motorola, Inc. As mentioned in United States Patent 20070142072, two way radios allow users the ability to wirelessly communicate with others on a small network. Most two way radios use various channels or frequencies for communication. Monitoring of more than one channel allows a user to communicate with a plurality of people for a variety of purposes. In a security environment, for instance, channel 1 may be used to communicate about and monitor emergency conditions. Channel 2 may be used to communicate about and monitor major security threats. Channel 3 may be used to communicate about and monitor minor security threats. A user may monitor all three channels by using a two way radio having a scanning mode. Other devices that can be used instead of two way radios include cellular telephones. These devices enable personal communication by allowing telephone access from anywhere within reach of wireless network infrastructure (e.g., cellular networks, communication satellites, or other infrastructure of other wireless networks adapted for voice communications). However, one restriction is that these devices are typically desktop devices or hand-held devices and thus do not provide hands-free communications capability.
Moreover, in as much as the use of handheld wireless voice communication devices is not restricted to homes and offices, such devices will often be used in environments where there is considerable ambient noise. Examples of such environments include busy urban settings, inside moving vehicles and on factory floors. Ambient noise in an environment can degrade the intelligibility of received voice audio and thereby interfere with users' ability to communicate.
U.S. Pat. No. 6,917,688 discloses an adaptive noise canceling microphone system for extracting a desired signal, in particular a desired speech signal, having two microphones being arranged at a predefined distance from each other; a signal forming system (SFS) being adapted to receive a first and second input signals resulting from sounds received by the two microphones wherein an acoustical signal component in the first input signal is determined, wherein an acoustical signal component in the second input signal is determined, wherein the acoustical signal component in the first input signal is enhanced to generate a speech enhanced signal, and wherein the acoustical signal component in the second input signal is suppressed to generate a speech nulled signal; an adaptive noise cancellation filtering circuit being adapted to receive the speech enhanced signal and the speech nulled signal, wherein the noise in the speech enhanced signal is cancelled using the speech nulled signal as reference, thereby generating an output filtered signal representing the desired signal.
United States Patent 20060270467 discusses enhancing the intelligibility of speech emitted into a noisy environment by filtering ambient noise with a filter that simulates the physical blocking of noise by at least a part of a voice communication device and determining a frequency dependent SNR of received voice audio relative to ambient noise is computed on a perceptual (e.g. Bark) frequency scale. Formants are identified and the SNR in bands including certain formants are modified with formant enhancement gain factors in order to improve intelligibility.
However, in certain industrial, emergency, government and military applications, such noise filtering is insufficient to provide high quality, hands-free, yet inconspicuous communication capability for field personnel.